Lecture #4 Date _________

• Chapter 9~Cellular

Respiration: Harvesting Chemical Energy

Things to Know• The difference between fermentation and cellular respiration

• The role of glycolysis in oxidizing glucose to 2 molecules of pyruvate

• The process that brings pyruvate from cytosol into the mitochondria and introduces it into the citric acid cycle

• How the process of chemiosis utilizes the electrons from NADH and FADH2 to produce ATP

Catabolic Pathways• Catabolic pathways – molecules are broken down and

their energy is released

2 Types of Catabolic Pathways

- fermentation – partial degradation of sugar without the use of oxygen

- cellular respiration – the most efficient catabolic pathway, where oxygen is used as a reactant with organic fuel (called aerobic respiration because it uses oxygen)

Some Background• Carbohydrates, fats and protein can all be broken down to

release energy in cell. resp., but glucose is the primary molecule used in cell. resp.

Here’s the equation:

C6H12O6 + 6 O6 6 CO2 + 6 H2O + Energy

The energy released from this is stored by phosphorylating (adding phosphate) ADP into ATP

Redox Reactions• The reactions in cell. resp. are a type called oxidation-

reduction (redox), where electrons are transferred from one reaction to another

- loss of electrons from reactant are called oxidation

- gain of electrons is

reduction

Redox in Cell. Resp.

C6H12O6 + 6 O6 6 CO2 + 6 H2O + Energy

NAD+ and NADH• NAD+ is an electron carrier• NAD+ accepts 2 electrons to form NADH

Cellular Respiration

• There are 3 steps to cellular respiration:- Glycolysis

- Citric Acid Cycle

- Oxidative Phosphorylation: electron transport & chemiosis

Glycolysis• Glycolysis occurs in the cytosol

(cytoplasm)• Glucose is broken down into 2

pyruvate acid molecules• In the “Energy Investment phase” 2

ATP are used• In the “Energy Payoff phase” 4 ATP

are produced• The Results: 2 ATP, 2 pyruvate acid,

2 NADH

Citric Acid Cycle (aka Kreb’s Cycle)

• Pyruvate acids use transport protein to enter the mitochondria

• In the process, pyruvate acid is converted by Coenzyme A to make Acetyl CoA

• Now this Acetyl CoA enters the citric acid cycle

Citric Acid Cycle (aka Kreb’s Cycle)• 2 Acetyl CoA enters the cycle and each

go into the cycle• Results (from 2 rounds): 4 CO2, 6

NADH, 2 FADH2, and 2 ATP produced• * note 1 glucose molecule (C6H12O6)

makes 2 rounds • **note CO2 released is what you

breathe out• *** note NADH and FADH2 are electron

carriers and will produce a bunch of ATP in Oxidative Phosphorylation

Oxidative PhosphorylationElectron Transport Chain

- embedded in the inner membrane of the mitochondria- 3 proteins work as hydrogen pumps- step by step process that pumps H+ that is powered by the electron carriers NADH and FADH2

- H2O is produced in Electron Transport Chain (NO ATP produced!!)

Oxidative PhosphorylationChemiosmosis

- the H+ ions are pumped back in chemiosmosis through a protein called the ATP Synthase

- ATP is produced from ADP in chemiosmosis

IN TOTAL

- Oxidative Phosphorylation produced 32-24 ATP- which means cellular respiration makes a total of 36-38 ATP (2 from Glycolysis and 2 from Kreb’s Cycle)

Review: Cellular Respiration

• Glycolysis: 2 ATP (substrate-level phosphorylation)

• Kreb’s Cycle: 2 ATP (substrate-level phosphorylation)

• Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP

• 38 TOTAL ATP/glucose

Fermentation• Fermentation is a process to make ATP without the presence of

oxygen• Glycolysis still occurs, but that’s the only similarity with cell. resp.• After glycolysis there’s 2 options:

- alcohol fermentation – pyruvate is converted to ethanol (alcohol), releasing CO2 and NADH- lactic acid fermentation – pyruvate is reduced by NADH and lactic acid is waste product

• Facultative anaerobes are organisms that prefer cell resp., but can do fermentation if no oxygen available